Functionalized graphene/polystyrene composite, green synthesis and characterization

A composite of sulfonated waste polystyrene (SWPS) and graphene oxide was synthetized by an inverse coprecipitation in-situ compound technology. Polystyrene (PS) has a wide range of applications due to its high mechanical property. the graphene were incorporated into sulfonated polystyrene (SPS) to improve the thermal stability and mechanical performance of the composites. Functionalized graphene were synthesized with tour method by using recovered anode (graphite) of dry batteries while sulfonated waste expanded polystyrene was obtained through sulfonation of the polymer. The SPS and GO + SPS composite were characterized using by Fourier Transform Infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). While the degree of sulfonation (DS) was determined through elemental analysis. The results show the degree of sulfonation of the composite is 23.5% and its ion exchange capacity is 1.2 meq g−1. TEM analysis revealed that the GO particles were loaded on the surface of sulphonated polystyrene and that the SWPS was intercalated into the sub-layers of nanoG homogeneously, which result in an increase in electrical conduction.

www.nature.com/scientificreports/ was then incorporated into the SWPS particles which can be used as ion exchange. Although ion exchange is one of the most efficient methods for heavy metal removal, with technologically simple operation, high efficiency and reliability. However, due to the high cost of ion exchange resins, the ion exchange process is not commonly used for industrial wastewater treatment. So using recycled materials as ion exchange resins are also a possible solution for cost reduction production and application of ion exchange resins The composite of sulfonated waste polystyrene and graphene oxide nanoparticles was synthesized and characterized.

Materials and methods
Extraction of graphite from waste dry cell batteries. The spent batteries were carefully disassembled without causing any damage to the graphite rods within. To remove the other chemicals adhered to the graphite rods, they were disassembled and thoroughly wiped and washed with distilled water. After drying, the electrodes were ground and crushed to produce a fine graphite powder. Further treatment of the graphite powder was carried out in a beaker, containing HCl and HNO 3 (3:1) and heated for 6 h. Finally, to get the pH back to normal, the sample was centrifuged and rinsed multiple times in distilled water.

Preparation of sulfonated polystyrene (SPS).
Waste EPS packaging material was collected washed, and air dried. It was ground in a seed mill until the pieces were from 3 to 7 mm wide with a thickness of 1 mm. The resulting polystyrene was sulfonated in two stages by reaction with acetyl sulfate in CH 2 Cl 2 , according to the following sulfonation process: Preparation of acetyl sulphate (sulfonation reagent). This step should be done freshly prior to the sulfonation reaction of PS. 12 mL of acetic acid anhydride were mixed with 24 mL of dichloroethane, in three-neck flask under nitrogen atmosphere. This solution is cooled to 0 °C in ice bath. Then, 6 mL of Oleum were added portionwise and stirred for 1 h while maintaining the temperature, resulting in 1 M of acetyl sulphate (homogeneous and clear solution). Note: during the preparation an excess of acetic anhydride were used to make sure that there are no water traces, and that the latter was completely converted to [acetyl sulphate]. Finally, the three-neck flask was capped, and the acetyl sulphate resulted in DCE solution was ready to be used.
Sulfonation reaction. 4 g of PS were completely dissolved with 200 mL of dichloroethane in a 500 mL threeneck flask, equipped with a condenser, mechanical stirring, thermometer and dropping funnel. The solution was stirred at 40 °C under a small nitrogen flow rate, until a homogenous solution is attained. As prepared 1 M acetyl sulphate was immediately transferred and added to the polymer solution at (40 °C) using a dropping funnel. The degree of sulfonation of PS was controlled by adjusting the sulfonation time from 1 to 6 h, the solution became clear yellow colour after the addition of sulfonating agent. The reaction was stopped by adding 10 mL of isopropanol to the mixture and allowing it to cool to room temperature. Next step was precipitation by dropping the prepared solution into a large volume of boiling deionized water. Followed by washing several times with deionized water to eliminate the solvent and hydrolyse the acetyl sulphate. Finally, the obtained powder was filtered and dried at (70 °C) in a vacuum oven for 3 days.

Synthesis of GO + SWPS composites.
Inverse coprecipitation in-situ compound method was used to form SPS/GO composites as shown in Fig. 1. 2 g SPS particles and 40 mL of 0.2 M NaOH solution were transferred to a 250 mL four-neck flask and kept at 80 °C for 30 min. Throughout the reaction, N 2 was bubbled. Then, using an ultrasonic disperse technique, 0.0164 g GO were dispersed into 60 mL 1:1 (V/V) ethanol-water mixed solvents. After that, the mixture was dropped into the above four-neck flask and vigorously stirred for 30 min at 80 °C. The suspension's colour changed to black almost instantly. When the dropping was done, the stirring was maintained at 50 °C for 1 h. The composite was isolated by centrifuge after cooling to room temperature, rinsed with deionized water until the solution was neutral, then dried under vacuum at 60 °C for 24 h 21 .

Results & discussion
Reaction scheme of homogeneous sulfonation. The sulphonation process occurs in two steps: Fig. 2 depicts the reaction involved in homogeneous sulfonation of PS, and Fig. 3 depicts the homogeneous sulfonation reaction scheme.
Sulfonation reaction might take longer than expected because of a side reaction for sulfonate synthesis induced by a crosslinking event that occurred between two sulfonic groups for distinct SPS units due to an intermolecular mechanism. Figure 4 depicts the crosslinking mechanism.    www.nature.com/scientificreports/ Tendency to the inter-molecular reaction is affected with several parameters including: 1. The sulfonic groups content will be increased by the elevating the concentration for the reaction sulfonating agent used with polymer solution. 2. Also elevating reaction temperature will lead to a higher percentage of the yields The best degree of sulfonation 30% was found to be achieved after 3 h 22 . Because both SPS and GO contain a large number of functional groups on their surfaces, it's possible to predict significant interactions between the two to cause composite production. Actually, as evidenced by the IR data described below, this is proven to be accurate. Figure 6  These results are in accordance with the TEM image of SPS/GO composite observation. In Fig. 7a, it can be seen that particles were loaded on the surface of sulphonated polystyrene exhibiting a homogeneous distribution with no aggregation compared to Fig. 7b of the GO which shows the linear deposit, exhibiting clear coagulation. The GO-SPS show the few-layered graphene oxide grafted with branches of SPS. This indicates that SPS particles are effectivlly coated by GO particles.  where C NaOH is the concentration of NaOH and M is the mass of SPS. As the number of sulfonic acid groups linked to the PS has increased, the SPS is more soluble in water and better able to interact with the graphene. As a result of the high degree of substitution of PS by sulfonic acid groups, the phenyl groups can exhibit a conjugation effect with sulfonic acid groups, confirmed by the increased electrical conductivity of the SWPS matrix. As the sulfonation increases, and the sulfonic groups interconnect result in the creation of ionic nanochannels. Those ionic nanochannels are critical for the transport and mechanical properties of the polymer 23 .
(1) DoS = V NaOH * C NaOH /M  www.nature.com/scientificreports/ DS depends largely on many factors such as the concentration of polymer, concentration of the sulfonating agent, the temperature and the time of sulfonation reaction. Indeed, the degree of sulfonation could be controlled by adjusting these parameters. It was clear that, as the sulfonation reaction time was increased, a noticeable increase in DS 24 .

Conclusions
A composite of graphene oxide (GO) and sulfonated polystyrene are prepared with enhanced properties. The manufacture of SPS was observed in the Fourier transform infrared spectra FT-IR as created function group peak vibration range. The properties of SPS are favourably manipulated by the incorporation of GO. Intermolecular interactions between the components in composite are established by FTIR. Composite is characterized by transmission electron microscopy (TEM) which showed the uniform distribution of GO particles in SPS matrix.
Because of the strong interaction between -SO 3 H functionality of SPS and functional group of GO, the SPS particles are adsorbed on the graphene surface. This results in stable SPS/GO composite. The composite display better thermal, mechanical and electrical conduction compared to polymer.
SPS particles help to produce and stabilize single layer graphene sheets; in turn these GO Sheets help to produce mechanically strong ion conducting SPS resin. This enhancement allows us to use it for waste water treatment as durable and efficient raw material able to stand in severs conditions. The method we proposed in this paper is a high standard method with several advantages, including the use of waste polystyrene, which reduces environmental pollution, avoids harmful gases, which are environmentally beneficial, and is a convenient and straightforward procedure that saves energy resources. We hope for more practical time leading us for more detail and results but COVID-19 waste mostly available time to finish this study.

Data availability
The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.